Elastomer composition having a very good dispersion of the charge in the elastomer matrix

ABSTRACT

The invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler including at least carbon black, having a specific surface area CTAB greater than or equal to 130 m2/g, a plasticizing hydrocarbon resin, the vitreous transition temperature of which, Tg, is greater than 20° C., and the softening point of which is less than 170° C., and a cross linking system, the dispersion of the filler in the elastomeric matrix having a Z score greater than or equal to 70.

This application is a 371 of PCT/EP2012/071280, filed 26 Oct. 2012,which claims benefit under 35 U. S. C. § 119 of the filing date ofFrench patent application 1159821, filed 28 Oct. 2011, the entirecontents of which is incorporated herein by reference for all purposes.

BACKGROUND 1. Field

The disclosure relates to a rubber composition in particular for a tiretread, and more particularly for a tire intended to equip vehiclescarrying heavy loads and running at sustained speeds, such as lorries,tractors, trailers or buses, aircraft, etc.

2. Description of Related Art

Some current tires, referred to as “road” tires, are intended to run athigh speed and over increasingly long journeys, as a result of theimprovement in the road network and of the growth of the motorwaynetwork throughout the world. However, since saving fuel and the need toprotect the environment have become a priority, it is important fortires to have a low energy consumption. One of the sources of energydissipation is the heating-up of the tire.

Likewise, it is known that the treads of tires used for civilengineering are particularly sensitive to increased temperature. As ithappens, an improvement in the properties of tires, and in particulartheir wear resistance, is continually sought and, conventionally, animprovement in wear resistance is known to be reflected by an increasein energy consumption.

In order to obtain such an improvement in wear resistance and energyconsumption, it is sought to use, in the tread, reinforcing fillerswhich are finer, in particular “fine” carbon blacks, i.e. carbon blackswhich have a CTAB specific surface area greater than or equal to 90m²/g, or even “very fine” blacks, i.e. carbon blacks having a CTABspecific surface area greater than or equal to 130 m²/g. However, inorder to obtain the optimum reinforcing and hysteresis propertiesimparted by a filler in a tire tread and thus high wear resistance andlow rolling resistance, it is generally known that this filler should bepresent in the elastomeric matrix in a final form that is both as finelydivided as possible and as uniformly distributed as possible. Suchconditions can be achieved only if this filler has a very good capacity,on the one hand, to be incorporated into the matrix during the mixingwith the elastomer and to deagglomerate, and, on the other hand, todisperse uniformly in this matrix.

As it happens, very fine blacks are known to be extremely difficult tocorrectly disperse in the elastomeric matrix and cause degradation ofprocessability (compared with the use of less fine blacks at equalcontent). One solution for those skilled in the art would be the use ofplasticizing oil or resin to improve processability. However, it isknown that the use of such plasticizing agents results in a veryconsiderable degradation of the energy at break properties (elongationat break and stress at break properties).

SUMMARY

The applicant has discovered, surprisingly, contrary to the knowledge ofthose skilled in the art, that the combination of very fine carbonblacks in rubber compositions exhibiting a very good dispersion of thefiller in the elastomeric matrix, and in the presence of certainspecific plasticizing resins, makes it possible both to obtain goodprocessability without degrading the limiting properties at break.

An embodiment of the invention is thus a rubber composition based on atleast one diene elastomer, a reinforcing filler comprising at leastcarbon black having a CTAB specific surface area greater than or equalto 130 m²/g, a plasticizing hydrocarbon resin, the glass transitiontemperature, Tg, of which is greater than 20° C. and the softening pointof which is less than 170° C., and also a crosslinking system, thedispersion of the filler in the elastomeric matrix having a Z scoregreater than or equal to 70.

Preferably, the plasticizing resin content of the composition rangesfrom 2 to 50 parts per hundred parts by weight of elastomer, preferablyfrom 5 to 25 phr.

According to one preferential embodiment of the invention, thecomposition is obtained from a first masterbatch comprising at least thediene elastomer and the carbon black, and having a dispersion of thecarbon black in the elastomeric matrix which has a Z score greater thanor equal to 80.

According to one variant of implementation of the invention, the firstmasterbatch is obtained by mixing, in the liquid phase, from a dieneelastomer latex and an aqueous dispersion of carbon black.

Indeed, there are various methods for obtaining a masterbatch of dieneelastomer and of reinforcing filler. In particular, one type of solutionconsists, for improving the dispersibility of the filler in theelastomeric matrix, in mixing the elastomer and the filler in the“liquid” phase. To do this, use is made of an elastomer in the form oflatex which is in the form of elastomer particles dispersed in water,and of an aqueous dispersion of the filler, i.e. a filler dispersed inwater, commonly referred to as “slurry”. Certain processes inparticular, such as those described in document U.S. Pat. No. 6,048,923,make it possible to obtain a masterbatch of elastomer and of fillerexhibiting a very good dispersion of the filler in the elastomericmatrix, greatly improved compared with the dispersion of the filler inthe elastomeric matrix capable of being obtained when elastomer andreinforcing filler are mixed in the solid phase. This process consistsin particular in incorporating a continuous stream of a first fluid madeup of an elastomer latex in the mixing zone of a coagulation reactor, inincorporating a second continuous stream of a second fluid made up of anaqueous dispersion of filler under pressure in the mixing zone so as toform a mixture with the elastomer latex, the mixing of these two fluidsbeing sufficiently energetic to make it possible to virtually completelycoagulate the elastomer latex with the filler before the outlet orificeof the coagulation reactor, and then in drying the coagulum obtained.

An embodiment of the invention is also a composition based on at leastone diene elastomer, a reinforcing filler comprising at least carbonblack having a CTAB specific surface area greater than or equal to 130m²/g, a plasticizing hydrocarbon resin, the glass transitiontemperature, Tg, of which is greater than 20° C. and the softening pointof which is less than 170° C., and also a crosslinking system, obtainedfrom a first masterbatch comprising at least the diene elastomer and thecarbon black, and exhibiting a dispersion of the carbon black in theelastomeric matrix which has a Z score greater than or equal to 80.

Preferably, the plasticizing resin content of the composition rangesfrom 2 to 50 parts per hundred parts by weight of elastomer, preferablyfrom 5 to 25 phr.

According to one preferential embodiment of the invention, thecomposition is obtained from a first masterbatch comprising at least thediene elastomer and the carbon black, and exhibiting a dispersion of thecarbon black in the elastomeric matrix which has a Z score greater thanor equal to 80.

According to one variant of implementation of the invention, the firstmasterbatch is obtained by mixing, in the liquid phase, from a dieneelastomer latex and an aqueous dispersion of carbon black, preferablyidentical to the liquid-phase process detailed previously.

An embodiment of the invention also relates to a process for preparing acomposition comprising at least one diene elastomer, a reinforcingfiller comprising at least carbon black having a CTAB specific surfacearea greater than or equal to 130 m²/g, a plasticizing hydrocarbonresin, the glass transition temperature, Tg, of which is greater than20° C. and the softening point of which is less than 170° C., and also acrosslinking system, the dispersion of the filler in the elastomericmatrix having a Z score greater than or equal to 70, which comprises thefollowing steps:

-   -   incorporation of all of the constituents of the composition,        with the exception of the crosslinking system, in a mixer by        thermomechanically kneading the whole mixture until a maximum        temperature of between 130° C. and 200° C. is reached,    -   cooling of the whole mixture to a temperature of less than 100°        C.,    -   subsequent incorporation of the crosslinking system,    -   kneading of the whole mixture until a maximum temperature of        less than 120° C. is reached.

Preferably, a first masterbatch comprising at least the diene elastomerand the carbon black, and exhibiting a dispersion of the carbon black inthe elastomeric matrix which has a Z score greater than or equal to 80,is prepared prior to the incorporation of all of the constituents of thecomposition in the mixer.

Even more preferentially, the masterbatch is prepared in the liquidphase from at least one elastomer latex and a dispersion of carbonblack, in particular according to the process detailed previously.

An embodiment of the invention also relates to a process for preparing acomposition comprising at least one diene elastomer, a reinforcingfiller comprising at least carbon black having a CTAB specific surfacearea greater than or equal to 130 m²/g, a plasticizing hydrocarbonresin, the glass transition temperature, Tg, of which is greater than20° C. and the softening point of which is less than 170° C., and also acrosslinking system, which comprises the following steps:

-   -   preparation of a first masterbatch comprising the diene        elastomer and the carbon black, this first masterbatch        exhibiting a dispersion of the filler in the elastomeric matrix        which has a Z score greater than or equal to 80,    -   incorporation of the other constituents of the composition, with        the exception of the crosslinking system, into the first        masterbatch in a mixer by thermomechanically kneading the whole        mixture until a maximum temperature of between 130° C. and        200° C. is reached,    -   cooling of the whole mixture to a temperature of less than 100°        C.,    -   subsequent incorporation of the crosslinking system,    -   kneading of the whole mixture until a maximum temperature of        less than 120° C. is reached.

Preferably, the masterbatch is prepared in the liquid phase from atleast one elastomer latex and a dispersion of carbon black, inparticular according to the process detailed previously.

An embodiment of the invention also relates to a masterbatch based on atleast one diene elastomer, a reinforcing filler comprising at leastcarbon black having a CTAB specific surface area greater than or equalto 130 m²/g, a plasticizing hydrocarbon resin, the glass transitiontemperature, Tg, of which is greater than 20° C. and the softening pointof which is less than 170° C., the dispersion of the filler in theelastomeric matrix having a Z score greater than or equal to 70.

Preferably, this masterbatch is obtained from a first masterbatchcomprising at least the diene elastomer and the carbon black, andexhibiting a dispersion of the carbon black in the elastomeric matrixwhich has a Z score greater than or equal to 80.

Even more preferentially, this first masterbatch is prepared in theliquid phase from at least one elastomer latex and a dispersion ofcarbon black, in particular according to the process detailedpreviously.

An embodiment of the invention also relates to a masterbatch based on atleast one diene elastomer, a reinforcing filler comprising at leastcarbon black having a CTAB specific surface area greater than or equalto 130 m²/g, a plasticizing hydrocarbon resin, the glass transitiontemperature, Tg, of which is greater than 20° C. and the softening pointof which is less than 170° C., obtained from a first masterbatchcomprising at least the diene elastomer and the carbon black, andexhibiting a dispersion of the carbon black in the elastomeric matrixwhich has a Z score greater than or equal to 80.

Preferably, this first masterbatch is prepared in the liquid phase fromat least one elastomer latex and a dispersion of carbon black, inparticular according to the process detailed previously.

Finally, an embodiment of the invention is a finished or semi-finishedarticle, a tire tread, a tire and a semi-finished product comprising acomposition as described previously or a masterbatch as describedpreviously.

In what follows, the term “masterbatch” is intended to mean anelastomer-based composite into which a filler and optionally otheradditives have been introduced.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Measurements and Tests

The rubber compositions are characterized, before and after curing, asindicated hereinafter.

Mooney Plasticity

Use is made of an oscillating consistometer as described in the Frenchstandard NF T 43-005 (1991). The Mooney plasticity measurement iscarried out according to the following principle: the composition in theuncured state (i.e. before curing) is moulded in a cylindrical chamberheated to 100° C. After preheating for one minute, the (small-sized)rotor rotates within the test specimen at 2 rpm and the working torquefor maintaining this movement is measured after rotating for 4 minutes.The Mooney plasticity (MS 1+4) is expressed in “Mooney units” (MU, with1 MU=0.83 Newton.metre).

Dispersion

As is known, the dispersion of filler in an elastomeric matrix can berepresented by the Z score, which is measured, after crosslinking,according to the method described by S. Otto et al. in Kautschuk GummiKunststoffe, 58th edition, NR 7-8/2005, in accordance with the standardISO 11345.

The calculation of the Z score is based on the percentage of surfacearea in which the filler is not dispersed (“% undispersed surfacearea”), as measured by the “disperGRADER+” machine provided with itsoperating instructions and its “disperDATA” operating software by thecompany Dynisco, according to the equation:

Z=100−(% undispersed surface area)/0.35

The percentage of undispersed surface area is, for its part, measured bya camera that observes the surface area of the sample under incidentlight at 30°. The light points are associated with filler andagglomerates, while the dark points are associated with the rubbermatrix; digital processing converts the image into a black and whiteimage, and enables the determination of the percentage of undispersedsurface area, as described by S. Otto in the abovementioned document.

The higher the Z score, the better the dispersion of the filler in theelastomeric matrix (a Z score of 100 corresponding to a perfectdispersion and a Z score of 0 to a mediocre dispersion). A Z scoregreater than or equal to 80 will be considered to correspond to asurface area having a very good dispersion of the filler in theelastomeric matrix.

Tensile Tests

These tensile tests make it possible to determine the elasticitystresses and the properties at break. Unless otherwise indicated, theyare carried out in accordance with the French standard NF T 46-002 ofSeptember 1988. At first elongation (i.e. after an accommodation cycleat the extension rate provided for the measurement itself), the nominalsecant modulus (or apparent stress, in MPa) is measured at 100%elongation (denoted MA100). The tensile measurements for determining thesecant accommodated moduli are carried out at a temperature of 23°C.+/−2° C., and under standard hygrometry conditions (50+/−5% relativehumidity).

The stress at breaks (in MPa) and the elongations at break (in %) arealso measured. All these tensile measurements are carried out at atemperature of 60° C.±2° C., and under standard hygrometry conditions(50±5% relative humidity), according to the French standard NF T 40-101(December 1979).

The energy at break is the product of the stress at break and theelongation at break.

Dynamic Properties

The dynamic properties and in particular tan(δ)_(max), representative ofthe hysteresis, are measured on a viscosity analyser (Metravib VA4000),according to the standard ASTM D 5992-96. The response of a sample ofvulcanized composition (cylindrical test specimen with a thickness of 4mm and a cross section of 400 mm²), subjected to a simple alternatingsinusoidal shear stress, at a frequency of 10 Hz, is recorded understandard temperature conditions (23° C.) according to the standard ASTMD 1349-99, or, as appropriate, at a different temperature; inparticular, in the examples cited, the measurement temperature is 60° C.A peak-to-peak strain amplitude sweep is carried out from 0.1% to 50%(forward cycle) and then from 50% to 0.1% (return cycle). The results ofwhich use is made are the complex dynamic shear modulus (G*) and theloss factor tan(δ). For the return cycle, the maximum value of tan(δ)observed, denoted tan(δ)_(max), is noted.

The invention relates to a composition based on at least one dieneelastomer, a reinforcing filler comprising at least carbon black havinga CTAB specific surface area greater than or equal to 130 m²/g, aplasticizing hydrocarbon resin, the glass transition temperature, Tg, ofwhich is greater than 20° C. and the softening point of which is lessthan 170° C., and also a crosslinking system, the dispersion of thefiller in the elastomeric matrix having a Z score greater than or equalto 70.

According to one embodiment of the invention, this composition isobtained from a first masterbatch comprising at least the dieneelastomer and the carbon black, and exhibiting a dispersion of the blackof 80.

In the present description, unless otherwise expressly indicated, allthe percentages (%) indicated are % by weight. Furthermore, any range ofvalues denoted by the expression “between a and b” represents the rangeof values from more than a to less than b (i.e. limits a and bexcluded), whereas any range of values denoted by the expression “from ato b” signifies the range of values from a up to b (i.e. including thestrict limits a and b).

Diene Elastomer

In a normal manner, the terms “elastomer” and “rubber”, which areinterchangeable, are used without distinction in the text.

The composition in accordance with the invention comprises at least onefirst diene elastomer and optionally a second elastomer identical to ordifferent from the first, which may or may not therefore be a dieneelastomer.

The term “diene” elastomer or rubber should be understood to mean, in aknown manner, an elastomer resulting at least partly (i.e. a homopolymeror a copolymer) from diene monomers (monomers bearing two conjugated orunconjugated, carbon-carbon double bonds).

These diene elastomers can be classified into two categories:“essentially unsaturated” or “essentially saturated”. The term“essentially unsaturated” is generally intended to mean a dieneelastomer resulting at least partly from conjugated diene monomershaving a content of units of diene origin (conjugated dienes) which isgreater than 15% (mol %); thus, diene elastomers such as butyl rubbersor copolymers of dienes and of alpha-olefins of EPDM type do not fallwithin the above definition and can in particular be described as“essentially saturated” diene elastomers (low or very low content ofunits of diene origin, always less than 15%). In the category of“essentially unsaturated” diene elastomers, the term “highlyunsaturated” diene elastomer is intended to mean in particular a dieneelastomer having a content of units of diene origin (conjugated dienes)which is greater than 50%.

Among these diene elastomers, natural rubber and synthetic elastomersare, moreover, distinguished.

The expression “synthetic diene elastomers capable of being used inaccordance with the invention” is intended to mean more particularly, interms of the expression “diene elastomer”:

(a)—any homopolymer obtained by polymerization of a conjugated dienemonomer having from 4 to 12 carbon atoms;(b)—any copolymer obtained by copolymerization of one or more conjugateddienes with one another or with one or more aromatic vinyl compoundshaving from 8 to 20 carbon atoms;(c)—a ternary copolymer obtained by copolymerization of ethylene and ofan α-olefin having 3 to 6 carbon atoms with a non-conjugated dienemonomer having from 6 to 12 carbon atoms, such as, for example, theelastomers obtained from ethylene and propylene with a non-conjugateddiene monomer of the abovementioned type, such as, in particular,1,4-hexadiene, ethylidenenorbornene or dicyclopentadiene;(d)—a copolymer of isobutene and of isoprene (butyl rubber) and also thehalogenated versions, in particular chlorinated or brominated versions,of this type of copolymer.

The following are suitable in particular as conjugated dienes:1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C₁-C₅alkyl)-1,3-butadienes, such as, for example, 2,3-dimethyl-1,3-butadiene,2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene,2-methyl-3-isopropyl-1,3-butadiene, an aryl-1,3-butadiene,1,3-pentadiene or 2,4-hexadiene. The following, for example, aresuitable as vinylaromatic compounds: styrene, ortho-, meta- orpara-methylstyrene, the “vinyltoluene” commercial mixture,para-(tert-butyl)styrene, methoxystyrenes, chlorostyrenes,vinylmesitylene, divinylbenzene or vinylnaphthalene.

The copolymers can contain between 99% and 20% by weight of diene unitsand between 1% and 80% by weight of vinylaromatic units. The elastomerscan have any microstructure, which depends on the polymerizationconditions used, in particular on the presence or absence of a modifyingand/or randomizing agent and on the amounts of modifying and/orrandomizing agent employed. The elastomers can, for example, be block,random, sequential or microsequential elastomers, and can be prepared indispersion or in solution; they can be coupled and/or star-branched orelse functionalized with a coupling and/or star-branching orfunctionalization agent. For coupling to carbon black, mention may bemade, for example, of functional groups comprising a C—Sn bond oraminated functional groups, such as aminobenzophenone, for example; forcoupling to an inorganic filler such as silica, mention may be made, forexample, of silanol functional groups or polysiloxane functional groupshaving a silanol end (as described, for example, in FR 2 740 778 or U.S.Pat. No. 6,013,718, and WO 2008/141702), alkoxysilane groups (asdescribed, for example, in FR 2 765 882 or U.S. Pat. No. 5,977,238),carboxylic groups (as described, for example, in WO 01/92402 or U.S.Pat. No. 6,815,473, WO 2004/096865 or US 2006/0089445) or else polyethergroups (as described, for example, in EP 1 127 909 or U.S. Pat. No.6,503,973, WO 2009/000750 and WO 2009/000752). As other examples offunctionalized elastomers, mention may also be made of elastomers (suchas SBR, BR, NR or IR) of the epoxidized type.

The following are suitable: polybutadienes and in particular thosehaving a content (mol %) of 1,2-units of between 4% and 80% or thosehaving a content (mol %) of cis-1,4-units of greater than 80%,polyisoprenes, butadiene/styrene copolymers and in particular thosehaving a Tg (glass transition temperature (Tg), measured according toASTM D3418) of between 0° C. and −70° C. and more particularly between−10° C. and −60° C., a styrene content of between 5% and 60% by weightand more particularly between 20% and 50%, a content (mol %) of1,2-bonds of the butadiene part of between 4% and 75%, and a content(mol %) of trans-1,4-bonds of between 10% and 80%, butadiene/isoprenecopolymers and in particular those having an isoprene content of between5% and 90% by weight and a Tg of −40° C. to −80° C., andisoprene/styrene copolymers and in particular those having a styrenecontent of between 5% and 50% by weight and a Tg of between −5° C. and−50° C. In the case of butadiene/styrene/isoprene copolymers, thosehaving a styrene content of between 5% and 50% by weight and moreparticularly between 10% and 40%, an isoprene content of between 15% and60% by weight and more particularly between 20% and 50%, a butadienecontent of between 5% and 50% by weight and more particularly between20% and 40%, a content (mol %) of 1,2-units of the butadiene part ofbetween 4% and 85%, a content (mol %) of trans-1,4-units of thebutadiene part of between 6% and 80%, a content (mol %) of 1,2-plus3,4-units of the isoprene part of between 5% and 70% and a content (mol%) of trans-1,4-units of the isoprene part of between 10% and 50%, andmore particularly any butadiene/styrene/isoprene copolymer having a Tgof between −5° C. and −70° C., are in particular suitable.

To summarize, the synthetic diene elastomer(s) according to theinvention is (are) preferably selected from the group of highlyunsaturated diene elastomers consisting of polybutadienes (abbreviatedto “BRs”), synthetic polyisoprenes (IRs), butadiene copolymers, isoprenecopolymers and blends of these elastomers. Such copolymers are morepreferentially selected from the group consisting of butadiene/styrenecopolymers (SBRs), isoprene/butadiene copolymers (BIRs),isoprene/styrene copolymers (SIRs) and isoprene/butadiene/styrenecopolymers (SBIRs).

As has been specified above, processes for mixing in the liquid phaseare preferentially used to make it possible to obtain masterbatchesbased on diene elastomer and carbon black having a very good dispersionof the carbon black in the elastomer. Thus, in particular for preparingthe first masterbatch of diene elastomer and carbon black, use will moreparticularly be made of a diene elastomer latex, the elastomer latexbeing a particular form of the elastomer which is in the form ofelastomer particles dispersed in water.

The invention therefore preferentially relates to the latexes of dieneelastomers, the diene elastomers being those defined previously.

More particularly, for the natural rubber (NR) which is particularlysuitable for the invention, this natural rubber exists in various formsas detailed in chapter 3 “Latex concentrates: properties andcomposition” by K. F. Gaseley, A. D. T. Gordon and T. D. Pendle in“Natural Rubber Science and Technology”, A. D. Roberts, OxfordUniversity Press—1988.

In particular, several forms of natural rubber latex are sold: thenatural rubber latexes referred to as “field latexes”, the naturalrubber latexes referred to as “concentrated natural rubber latexes”,epoxidized latexes (ENR), deproteinized latexes or else prevulcanizedlatexes. The natural rubber field latex is a latex in which ammonia hasbeen added to prevent premature coagulation and the concentrated naturalrubber latex corresponds to a field latex that has undergone a treatmentcorresponding to a washing followed by a further concentration. Thevarious categories of concentrated natural rubber latexes are listed inparticular according to the standard ASTM D 1076-06.

Distinguished in particular from among these concentrated natural rubberlatexes are the concentrated natural rubber latexes of “HA” (highammonia) quality and of “LA” quality; for the invention, use willadvantageously be made of concentrated natural rubber latexes of HAquality.

The NR latex may be physically or chemically modified beforehand(centrifugation, enzymatic treatment, chemically modified, etc.).

The latex may be used directly or may be first diluted in water tofacilitate the processing thereof.

Thus, as synthetic elastomer latex, the latex may in particular consistof a synthetic diene elastomer already available in the form of anemulsion (for example a copolymer of butadiene and of styrene, SBR,prepared in emulsion) or of a synthetic diene elastomer initially insolution (for example an SBR prepared in solution), which is emulsifiedin a mixture of organic solvent and water, generally by means of asurfactant.

Particularly suitable for the invention is an SBR latex, in particularan SBR prepared in emulsion (ESBR) or an SBR prepared in solution(SSBR), and more particularly an SBR prepared in emulsion.

There are two main types of processes for emulsion copolymerization ofstyrene and butadiene, one of them, or the hot process (carried out at atemperature close to 50° C.), being suitable for the preparation ofhighly branched SBRs whereas the other, or the cold process (carried outat a temperature which may range from 15° C. to 40° C.), makes itpossible to obtain more linear SBRs.

For a detailed description of the effectiveness of several emulsifiersthat can be used in said hot process (as a function of the contents ofsaid emulsifiers), reference may, for example, be made to the twoarticles by C. W. Carr, 1. M. Kolthoff, E. J. Meehan, University ofMinesota, Minneapolis, Minesota which were published in Journal ofPolymer Science of 1950, Vol. V, no 2, pp. 201-206, and of 1951, Vol.VI, no 1, pp. 73-81.

Regarding comparative examples of the implementation of said coldprocess, reference may, for example, be made to the article ½ Industrialand Engineering Chemistry, 1948, Vol. 40, no 5, pp. 932-937, E. J.Vandenberg, G. E. Hulse, Hercules Powder Company, Wilmington, Del.+ andto the article ½ Industrial and Engineering Chemistry, 1954, Vol. 46, no5, pp. 1065-1073, J. R. Miller, H. E. Diem, B. F. Goodrich Chemical Co.,Akron, Ohio+.

In the case of an SBR elastomer (ESBR or SSBR), use is in particularmade of an SBR having an average styrene content, for example of between20% and 35% by weight, or a high styrene content, for example from 35%to 45%, a content of vinyl bonds of the butadiene part of between 15%and 70%, a content (mol %) of trans-1,4-bonds of between 15% and 75% anda Tg of between −10° C. and −55° C.; such an SBR may be advantageouslyused as a blend with a BR that preferably has more than 90% (mol %) ofcis-1,4-bonds.

It will be noted that it is possible to envisage using one or morenatural rubber latexes as a blend, or one or more synthetic rubberlatexes as a blend, or a blend of one or more natural rubber latexeswith one or more synthetic rubber latexes.

As the second elastomer of the composition, where appropriate, when itis not a diene elastomer, non-diene butyl elastomers such aspoly(isobutylene) homopolymers or poly(isobutylene)-based copolymers (ofcourse, if copolymers with isoprene are involved, it is a question ofthe diene elastomers previously described), and also the halogenatedderivatives, in particular generally brominated or chlorinatedderivatives, of these poly(isobutylene) homopolymers andpoly(isobutylene)-based copolymers, are in particular suitable.

Also suitable among the non-diene elastomers are copolymers ofisobutylene and of styrene derivatives, such as brominatedisobutylene/methylstyrene copolymers (BIMSs), one of which is inparticular the elastomer called EXXPRO, sold by the company Exxon. Asnon-diene elastomer particularly suitable for the invention, mention mayalso be made of non-diene thermoplastic elastomers (TPEs).

Advantageously, the weight fraction of the first diene elastomer in theelastomeric matrix is greater than or equal to 50% and preferablygreater than or equal to 60%.

Fillers

An organic filler consisting of carbon black is used as reinforcingfiller. All reinforcing carbon blacks having a CTAB specific surfacearea greater than or equal to 130 m²/g, and even more particularlycarbon blacks having a CTAB surface area greater than or equal to 160m²/g, are suitable as carbon blacks.

It should be specified that the CTAB specific surface area is determinedaccording to the French standard NF T 45-007 of November 1987 (methodB).

It is possible to combine with this carbon black, as a blend, one ormore organic fillers, such as, for example, functionalizedpolyvinylaromatic organic fillers, as described in applicationsWO-A-2006/069792 and WO-A-2006/069793, and/or one or more reinforcinginorganic fillers such as silica.

Thus, the term “inorganic filler” should be understood here, in a knownmanner, to mean any inorganic or mineral filler, whatever its colour andits origin (natural or synthetic), also referred to as “white filler”,“clear filler” or alternatively “non-black filler” as opposed to carbonblack, this inorganic filler being capable of reinforcing, by itself,without means other than an intermediate coupling agent, a rubbercomposition intended for the manufacture of a tread for tires, in otherwords capable of replacing, in its reinforcing role, a conventionaltire-grade carbon black for a tread. Such a filler is generallycharacterized by the presence of functional groups, in particularhydroxyl (—OH) groups, at its surface, requiring, in order to be used asa reinforcing filler, the use of a coupling agent or system intended toprovide a stable chemical bond between the isoprene elastomer and saidfiller.

Such an inorganic filler can therefore be used with a coupling agent inorder to enable the reinforcement of the rubber composition in which itis included. It can also be used with a covering agent (which does notprovide a bond between the filler and the elastomeric matrix) inaddition to a coupling agent or not (in this case the inorganic fillerdoes not play a reinforcing role).

The physical state in which the inorganic filler is present is notimportant, whether it is in the form of a powder, of microbeads, ofgranules, of balls or any other appropriate densified form. Of course,the term “inorganic filler” is also intended to mean mixtures of variousinorganic fillers, in particular highly dispersible siliceous and/oraluminous fillers as described hereinafter.

Mineral fillers of the siliceous type, in particular silica (SiO₂), orof the aluminous type, in particular alumina (Al₂O₃), are suitable inparticular as inorganic fillers. The silica used may be any silica knownto those skilled in the art, in particular any precipitated or fumedsilica having a BET specific surface area and also a CTAB specificsurface area that are both less than 450 m²/g, preferably from 30 to 400m²/g. Mention will be made, as highly dispersible precipitated silicas(HDSs), for example, of the Ultrasil 7000 and Ultrasil 7005 silicas fromthe company Evonik, the Zeosil 1165MP, 1135MP and 1115MP silicas fromthe company Rhodia, the Hi-Sil EZ150G silica from the company PPG, theZeopol 8715, 8745 and 8755 silicas from the company Huber, and thesilicas with a high specific surface area as described in application WO03/16837.

It is also possible to envisage the addition, to the carbon black, offillers such as carbon blacks partially or completely covered withsilica by a post-treatment, or carbon blacks modified in situ withsilica, such as, with no implied limitation, the fillers which are soldby the company Cabot Corporation under the name Ecoblack™ “CRX 2000” or“CRX4000”.

Preferentially, the content of total filler (carbon black and inorganicfiller such as silica) is between 20 and 200 phr, more preferentiallybetween 30 and 150 phr and even more preferentially between 30 and 100phr, the optimum being, in a known manner, different depending on theparticular applications targeted: the level of reinforcement expected ona bicycle tire, for example, is of course less than that required on atire capable of running at high speed in a sustained manner, for examplea motorcycle tire, or a tire for a passenger vehicle or for a utilityvehicle such as a heavy goods vehicle.

According to one preferential embodiment of the invention, use is madeof carbon black of which the content ranges from 20 to 80 phr, and itcan preferably be combined with an inorganic filler, in particularsilica, the content of which ranges from 5 to 50 phr, more particularlythe total filler of the composition comprising carbon black of which thecontent ranges from 35 to 70 phr and an inorganic filler, in particularsilica, of which the content ranges from 5 to 35 phr, even morepreferentially the total filler comprising carbon black of which thecontent ranges from 40 to 65 phr and an inorganic filler, in particularsilica, of which the content ranges from 10 to 30 phr.

Plasticizing Hydrocarbon Resin

The rubber compositions of the invention use a plasticizing hydrocarbonresin of which the Tg, glass transition temperature, is greater than 20°C. and of which the softening point is less than 170° C., as explainedin detail hereinafter.

In a manner known to those skilled in the art, the name “plasticizingresin” is reserved in the present application, by definition, for acompound which is, on the one hand, solid at ambient temperature (23°C.) (as opposed to a liquid plasticizing compound such as an oil), and,on the other hand, compatible (i.e. miscible at the content used,typically greater than 5 phr) with the rubber composition for which itis intended, so as to act as an actual diluting agent.

The hydrocarbon resins are polymers well known to those skilled in theart, miscible therefore by nature in the compositions of elastomer(s)when they are additionally described as “plasticizing”.

They have been widely described in the patents or patent applicationscited in the introduction of the present report, and also, for example,in the book entitled “Hydrocarbon Resins” by R. Mildenberg, M. Zanderand G. Collin (New York, V C H, 1997, ISBN 3-527-28617-9), chapter 5 ofwhich is devoted to their applications, in particular in the tire rubberfield (5.5. “Rubber Tires and Mechanical Goods”).

They can be aliphatic, naphthenic, aromatic or else of thealiphatic/naphthenic/aromatic type, i.e. based on aliphatic and/ornaphthenic and/or aromatic monomers. They can be natural or synthetic,based or not based on petroleum (if such is the case, also known aspetroleum resins). They are preferentially exclusivelyhydrocarbon-based, i.e. they comprise only hydrogen and carbon atoms.

Preferably, the plasticizing hydrocarbon resin has at least one, morepreferentially all, of the following characteristics:

-   -   a number-average molecular weight (Mn) of between 400 and 2000        g/mol;    -   a polydispersity index (PI) of less than 3 (as a reminder:        PI=Mw/Mn with Mw being the weight-average molecular weight).

More preferentially, this plasticizing hydrocarbon resin has at leastone, even more preferentially all, of the following characteristics:

-   -   a Tg of greater than 30° C.;    -   a weight Mn of between 500 and 1500 g/mol;    -   a PI index of less than 2.

The glass transition temperature Tg is measured in a known manner by DSC(Differential Scanning Calorimetry), according to the standard ASTMD3418 (1999), and the softening point is measured according to thestandard ASTM E-28.

The macrostructure (Mw, Mn and PI) of the hydrocarbon resin isdetermined by size exclusion chromatography (SEC): solventtetrahydrofuran; temperature 35° C.; concentration 1 g/l; flow rate 1ml/min; solution filtered on a filter with a porosity of 0.45 μm beforeinjection; Moore calibration with polystyrene standards; set of 3“WATERS” columns in series (“STYRAGEL” HR4E, HR1 and HR0.5); detectionby differential refractometer (“WATERS 2410”) and its associatedexploitation software (“WATERS EMPOWER”).

According to one particularly preferential embodiment, the plasticizinghydrocarbon resin is selected from the group consisting ofcyclopentadiene (abbreviated to CPD) or dicyclopentadiene (abbreviatedto DCPD) homopolymer or copolymer resins, terpene homopolymer orcopolymer resins, C5 fraction homopolymer or copolymer resins, andmixtures of these resins.

Among the above copolymer resins, use is preferentially made of thoseselected from the group consisting of (D)CPD/vinylaromatic copolymerresins, (D)CPD/terpene copolymer resins, (D)CPD/C5 fraction copolymerresins, terpene/vinylaromatic copolymer resins, C5fraction/vinylaromatic copolymer resins, and mixtures of these resins.

The term “terpene” combines here, in a known manner, alpha-pinene,beta-pinene and limonene monomers; use is preferentially made of alimonene monomer, which compound exists, in a known manner, in the formof three possible isomers: L-limonene (levorotatory enantiomer),D-limonene (dextrorotatory enantiomer), or else dipentene, a racemate ofthe dextrorotatory and levorotatory enantiomers.

Suitable as a vinylaromatic monomer are, for example, styrene,alpha-methylstyrene, ortho-methylstyrene, meta-methylstyrene,para-methylstyrene, vinyltoluene, para-(tert-butyl)styrene,methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene,vinylnaphthalene or any vinylaromatic monomer resulting from a C₉fraction (or more generally from a C₈ to C₁₀ fraction). Preferably, thevinylaromatic compound is styrene or a vinylaromatic monomer resultingfrom a C₉ fraction (or more generally from a C₈ to C₁₀ fraction).Preferably, the vinylaromatic compound is the minor monomer, expressedas molar fraction, in the copolymer under consideration.

According to one more particularly preferential embodiment, theplasticizing hydrocarbon resin is selected from the group consisting of(D)CPD homopolymer resins, (D)CPD/styrene copolymer resins, polylimoneneresins, limonene/styrene copolymer resins, limonene/(D)CPD copolymerresins, C5 fraction/styrene copolymer resins, C5 fraction/C9 fractioncopolymer resins, and mixtures of these resins.

The preferential resins above are well known to those skilled in the artand are commercially available, for example sold, as regards the:

-   -   polylimonene resins: by the company DRT under the name        “Dercolyte L120” (Mn=625 g/mol; Mw=1010 g/mol; PI=1.6; Tg=72°        C.) or by the company Arizona under the name “Sylvagum TR7125C”        (Mn=630 g/mol; Mw=950 g/mol; PI=1.5; Tg=70° C.);    -   C₅ fraction/vinylaromatic, in particular C₅ fraction/styrene or        C₅ fraction/C₉ fraction, copolymer resins: by Neville Chemical        Company under the names “Super Nevtac 78”, “Super Nevtac 85” or        “Super Nevtac 99”, by Goodyear Chemicals under the name        “Wingtack Extra”, by Kolon under the names “Hikorez T1095” and        “Hikorez T1100”, or by Exxon under the names “Escorez 2101” and        “ECR 373”;    -   limonene/styrene copolymer resins: by DRT under the name        “Dercolyte TS 105”, or by Arizona Chemical Company under the        names “ZT115LT” and “ZT5100”.

The content of hydrocarbon resin is preferentially between 2 and 35 phr.Below the minimum indicated, the technical effect targeted may prove tobe insufficient, whereas above the maximum, the bonding power of thecompositions in the uncured state, on the mixing tools, may in certaincases become totally unacceptable from an industrial point of view. Thecontent of hydrocarbon resin is even more preferentially between 5 and25 phr.

Masterbatches—Rubber Composition

Advantageously, the masterbatches and the compositions thus produced arecapable of being used in tire applications.

The rubber compositions for tires based on masterbatches and inorganicfiller according to the invention may also comprise, in a known manner,a coupling agent and/or a covering agent and a vulcanization system.

In order to couple the reinforcing inorganic filler to the dieneelastomer, use is made, in a known manner, of an at least bifunctionalcoupling agent (or bonding agent) intended to provide a sufficientconnection, of chemical and/or physical nature, between the inorganicfiller (surface of its particles) and the diene elastomer, in particularbifunctional organosilanes or polyorganosiloxanes.

Use is in particular made of silane polysulphides, referred to as“symmetrical” or “asymmetrical” depending on their specific structure,as described, for example, in applications WO 03/002648 (or US2005/016651) and WO 03/002649 (or US 2005/016650).

Suitable in particular, without the definition hereinafter beinglimiting, are silane polysulphides, referred to as “symmetrical”,corresponding to the following general formula (III):

Z-A-S_(x)-A-Z, in which:  (III)

-   -   x is an integer from 2 to 8 (preferably from 2 to 5);    -   A is a divalent hydrocarbon radical (preferably C₁-C₁₈ alkylene        groups or C₆-C₁₂ arylene groups, more particularly C₁-C₁₀,        especially C₁-C₄, alkylenes, in particular propylene);    -   Z corresponds to one of the formulae hereinafter:

-   -   in which:        -   the R¹ radicals, which are substituted or unsubstituted and            identical to or different from one another, represent a            C₁-C₁₈ alkyl, C₅-C₁₈ cycloalkyl or C₆-C₁₈ aryl group            (preferably C₁-C₆ alkyl, cyclohexyl or phenyl groups, in            particular C₁-C₄ alkyl groups, more particularly methyl            and/or ethyl);        -   the R² radicals, which are substituted or unsubstituted and            identical to or different from one another, represent a            C₁-C₁₈ alkoxyl group or a C₅-C₁₈ cycloalkoxyl group            (preferably a group selected from C₁-C₈ alkoxyls and C₅-C₈            cycloalkoxyls, even more preferentially a group selected            from C₁-C₄ alkoxyls, in particular methoxyl and ethoxyl).

In the case of a mixture of alkoxysilane polysulphides corresponding toformula (III) above, in particular the usual commercially availablemixtures, the mean value of the “x” subscripts is a fractional numberpreferably between 2 and 5, more preferentially close to 4. However, theinvention may also advantageously be carried out, for example, withalkoxysilane disulphides (x=2).

As examples of silane polysulphides, mention will more particularly bemade of bis((C₁-C₄)alkoxyl(C₁-C₄)alkylsilyl(C₁-C₄)alkyl) polysulphides(in particular disulphides, trisulphides or tetrasulphides), such as,for example, bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl)polysulphides. Among these compounds, use is in particular made ofbis(3-triethoxysilylpropyl) tetrasulphide, abbreviated to TESPT, offormula [(C₂H₅O)₃Si(CH₂)₃S₂]₂ or bis(triethoxysilylpropyl) disulphide,abbreviated to TESPD, of formula [(C₂H₅O)₃Si(CH₂)₃S]₂. Mention will alsobe made, as preferential examples, ofbis(mono(C₁-C₄)alkoxydi(C₁-C₄)alkylsilylpropyl) polysulphides (inparticular disulphides, trisulphides or tetrasulphides), moreparticularly bis(monoethoxydimethyl-silylpropyl) tetrasulphide asdescribed in patent application WO 02/083782 (or US 2004/132880).

As coupling agents other than an alkoxysilane polysulphide, mention willin particular be made of bifunctional POSs (polyorganosiloxanes) or elseof hydroxysilane polysulphides (R²=OH in formula III above), asdescribed in patent applications WO 02/30939 (or U.S. Pat. No.6,774,255) and WO 02/31041 (or US 2004/051210), or else silanes or POSsbearing azodicarbonyl functional groups, as described, for example, inpatent applications WO 2006/125532, WO 2006/125533, and WO 2006/125534.

As covering agents, consideration will generally be given to processingaids that are capable, in a known manner, owing to an improvement in thedispersion of the inorganic filler in the rubber matrix and a loweringof the viscosity of the compositions, of improving their ability toprocess in the uncured state, these processing aids being, for example,hydrolysable silanes, such as alkylalkoxysilanes (in particularalkyltriethoxysilanes), polyols, polyethers (for example polyethyleneglycols), primary, secondary or tertiary amines (for exampletrialkanolamines), hydroxylated or hydrolysable POSs, for exampleα,ω-dihydroxypolyorganosiloxanes (in particularα,ω-dihydroxypolydimethylsiloxanes), and fatty acids such as, forexample, stearic acid.

In the rubber compositions in accordance with the invention, the contentof coupling agent is preferentially between 0.1% and 12% by weight ofthe inorganic filler for a CTAB surface area of 160 m²/g, morepreferentially between 4% and 10% by weight of the inorganic filler fora CTAB surface area of 160 m²/g; and/or the content of covering agent ispreferentially between 0.1% and 20% by weight of the inorganic fillerfor a CTAB surface area of 160 m²/g, more preferentially between 5% and20% by weight of the inorganic filler for a CTAB surface area of 160m²/g. It is possible for the content of coupling agent to be adjusted tothe specific surface area level of the filler.

Those skilled in the art will understand that a filler of anothernature, in particular organic nature, might be used as filler equivalentto the inorganic filler described in the present section, provided thatthis filler is covered with an inorganic layer, such as silica, or elsecomprises, at its surface, functional sites, in particular hydroxyls,requiring the use of a coupling agent in order to form the connectionbetween the filler and the elastomer.

These rubber compositions in accordance with the invention may alsocomprise all or some of the standard additives customarily used inelastomeric compositions intended for the manufacture of tires, inparticular treads, such as, for example, other plasticizers, pigments,protective agents such as antiozone waxes, chemical antiozonants,antioxidants, anti-fatigue agents, reinforcing resins, methyleneacceptors (for example phenolic-novolac resin) or methylene donors (forexample HMT or H3M) as described, for example, in application WO02/10269, a crosslinking system based either on sulphur or on sulphurdonors, and/or on a peroxide and/or on bismaleimides, and vulcanizationaccelerators.

It will be noted that it is also possible to envisage producing themasterbatches in accordance with the invention by incorporating therein,in particular before the drying phase of the production of themasterbatch in the liquid phase, additives as described previously,antioxidant, coupling agent, covering agent, etc.

Manufacture of the Rubber Compositions and Masterbatches

The rubber compositions of the invention are manufactured in appropriatemixers, using two successive phases of preparation according to ageneral procedure well known to those skilled in the art: a first phaseof thermomechanical working or kneading (sometimes referred to as“non-productive” phase) at high temperature, up to a maximum temperatureof between 130° C. and 200° C., preferably between 145° C. and 185° C.,followed by a second phase of mechanical working (sometimes referred toas “productive” phase) at a lower temperature, typically less than 120°C., for example between 60° C. and 100° C., during which finishing phasethe crosslinking or vulcanization system is incorporated.

According to one preferential embodiment of the invention, all the baseconstituents of the compositions of the invention, with the exception ofthe vulcanization system, are incorporated intimately, by kneading,during the “non-productive” first phase, that is to say at least thesevarious base constituents are introduced into the mixer andthermomechanically kneaded, in one or more steps, until the maximumtemperature of between 130° C. and 200° C., preferably between 145° C.and 185° C., is reached.

According to one preferential embodiment of the invention, theplasticizing hydrocarbon resin and also the base constituents of thecompositions of the invention, with the exception of the vulcanizationsystem, in particular, where appropriate, the inorganic filler such assilica, are incorporated into the diene elastomer and the carbon blackwhich have been previously prepared in the form of a first masterbatch.

Preferentially, this first masterbatch is produced in the “liquid”phase. To do this, the process involves the diene elastomer in latexform, which is in the form of elastomer particles dispersed in water,and an aqueous dispersion of the carbon black, that is to say a fillerdispersed in water, commonly referred to as “slurry”. Even morepreferentially, the process steps described in document U.S. Pat. No.6,048,923 will be followed, which process consists in particular inincorporating a continuous stream of a first fluid consisting of theelastomer latex into the mixing zone of a coagulation reactor, inincorporating a second continuous stream of a second fluid consisting ofthe aqueous dispersion of carbon black under pressure into the mixingzone to form a mixture with the elastomer latex; the mixing of these twofluids being sufficiently energetic to make it possible to almostcompletely coagulate the elastomer latex with the carbon black beforethe outlet orifice of the coagulation reactor, and then in drying thecoagulum obtained.

According to another preferential embodiment of the invention, theinorganic filler and the second elastomer are incorporated into thefirst masterbatch while being likewise in the form of a secondmasterbatch that will have been prepared beforehand. This secondmasterbatch can be prepared in particular in solid form bythermomechanical kneading of the second elastomer and the inorganicfiller; it can also be prepared by any other process, and in particularit can also be prepared in the liquid phase.

It will be noted in particular that, in the case of the incorporation ofa second elastomer and/or of an inorganic filler, this or theseincorporation(s) can be carried out simultaneously with the introductioninto the mixer of the other constituents (in particular the first dieneelastomer or first masterbatch) but also advantageously that this orthese incorporation(s) may be offset in time by a few tens of seconds toa few minutes. It will be noted that, in the case of an addition of aninorganic filler and of a second elastomer, they may be introducedseparately or in the form of a second masterbatch containing the secondelastomer and the inorganic filler. In the case of the introduction ofthe second elastomer alone and of the inorganic filler alone, offset intime by a few tens of seconds to a few minutes, the inorganic filler maybe introduced before, after or simultaneously with the second elastomer.

By way of example, the (non-productive) first phase is carried out in asingle thermomechanical step during which all the necessary constituents(where appropriate in the form of a masterbatch as specifiedpreviously), the optional supplementary covering agents or processingaids and various other additives, with the exception of thevulcanization system, are introduced into an appropriate mixer, such asa standard internal mixer. The total duration of the kneading, in thisnon-productive phase, is preferably between 1 and 15 min. After coolingof the mixture thus obtained during the non-productive first phase, thevulcanization system is then incorporated at low temperature, generallyin an external mixer such as an open mill; everything is then mixed(productive phase) for a few minutes, for example between 2 and 15 min.

The crosslinking system is preferentially a vulcanization system, i.e. asystem based on sulphur (or on a sulphur donor) and on a primaryvulcanization accelerator. Added to this base vulcanization system arevarious known secondary vulcanization accelerators or vulcanizationactivators, such as zinc oxide, stearic acid or equivalent compounds, orguanidine derivatives (in particular diphenylguanidine), incorporatedduring the non-productive first phase and/or during the productivephase, as described subsequently.

The sulphur is used at a preferential content of between 0.5 and 12 phr,in particular between 1 and 10 phr. The primary vulcanizationaccelerator is used at a preferential content of between 0.5 and 10 phr,more preferentially between 0.5 and 5.0 phr.

Use may be made, as (primary or secondary) accelerator, of any compoundcapable of acting as accelerator for the vulcanization of dieneelastomers in the presence of sulphur, in particular accelerators of thethiazole type, and also derivatives thereof, and accelerators of thiuramor zinc dithiocarbamate type. These accelerators are, for example,selected from the group consisting of 2-mercaptobenzothiazyl disulphide(abbreviated to “MBTS”), tetrabenzylthiuram disulphide (“TBZTD”),N-cyclohexyl-2-benzothiazyl sulphenamide (“CBS”),N,N-dicyclohexyl-2-benzothiazyl sulphenamide (“DCBS”),N-(tert-butyl)-2-benzothiazyl sulphenamide (“TBBS”),N-(tert-butyl)-2-benzothiazyl sulphenimide (“TBSI”), zincdibenzyldithiocarbamate (“ZBEC”) and mixtures of these compounds.

The resulting final composition is then calendered, for example in theform of a sheet or slab, in particular for laboratory characterization,or else extruded in the form of a rubber profiled element that can beused, for example, as a tire tread for a passenger vehicle, a heavygoods vehicle, etc.

III Examples

The examples illustrate the improvement in the properties in terms ofprocessability and properties at break of rubber compositions inaccordance with the invention compared with control rubber compositionswhich differ from the compositions of the invention either through theCTAB specific surface area of the carbon black, or through the absenceof plasticizing hydrocarbon resin, or finally through the poordispersion (Z score) of the carbon black in the composition.

Some of the rubber compositions which follow were prepared from amasterbatch, produced in the liquid phase, of natural rubber and ofcarbon black, and others were prepared by mixing in the solid phase.

Preparation of Masterbatch of Natural Rubber and Carbon Black

The masterbatches of diene elastomer and carbon black used in some ofthe compositions which follow are produced in the liquid phase accordingto the process described in U.S. Pat. No. 6,048,923.

Thus, masterbatches are prepared, according to the protocol explained indetail in the abovementioned patent, from respectively carbon black N234and carbon black N134 sold by the company Cabot Corporation, and fromnatural rubber field latex originating from Malaysia and having a rubbersolid content of 28% and an ammonia content of 0.3%.

Masterbatches A of natural rubber and carbon black (with the N234 carbonblack or the N134 carbon black) are thus obtained in which the contentof carbon black is 50 phr.

Preparation of the Rubber Compositions

The control compositions TM are produced according to a conventionalprocess for mixing in solid form in which the elastomer, thereforenatural rubber in these examples, and the reinforcing filler,respectively according to the compositions: N234 carbon black and N134carbon black, sold by the company Cabot Corporation.

The control rubber compositions CA are produced from the masterbatch A(including N234 carbon black or N134 carbon black).

The various compositions are produced in the following way:

The tests below are carried out in the following way: introduced into aninternal mixer, filled to 70%, and the initial vessel temperature ofwhich is approximately 90° C., are the natural rubber in solid form andthe carbon black for the TM compositions or the masterbatch A for the CAcompositions, and the various other ingredients with the exception ofthe vulcanization system. Thermomechanical working (non-productivephase) is then carried out in one step (total duration of the kneadingequal to approximately 5 min), until a maximum “dropping” temperature ofapproximately 165° C. is reached.

The resulting mixture is recovered and cooled and then the vulcanizationsystem (sulphur and sulphenamide accelerator) is added in an externalmixer (homofinisher) at 70° C., by mixing the whole mixture (productivephase) for approximately 5 to 6 min.

The resulting compositions are then calendered either in the form ofslabs (thickness of 2 to 3 mm) or thin sheets of rubber for themeasurement of their physical or mechanical properties, or in the formof profiled elements that can be used directly, after cutting and/orassembly to/at the desired dimensions, for example as semi-finishedproducts for tires, in particular as tire treads.

3 Tests

The rubber composition TM1 is prepared “in bulk” from natural rubber andcarbon black in solid form as described in detail in section III-2; thecompositions CA1 and CA2 not in accordance with the invention and thecompositions CA3 to CA5 in accordance with the invention are preparedfrom the masterbatches A according to the process described in detail insection 111-2.

All of the compositions, whatever the manufacturing process, have thefollowing base formulation (in phr)

natural rubber 100 6PPD (a) 1.5 stearic acid 2 zinc oxide (c) 3accelerator (d) 1.4 sulphur 1.4 (a)N-1,3-dimethylbutyl-N-phenyl-para-phenylenediamine (“Santoflex 6-PPD”from the company Flexsys); (c) zinc oxide (industrial grade - from thecompany Umicore); (d) N-cyclohexyl-2-benzothiazyl sulphenamide(“Santocure CBS” from the company Flexsys).

In addition to these constituents, the TM and CA compositions differfrom one another by virtue of their Z score, the nature of the carbonblack and the nature and presence of plasticizing resin, and also itscontent, as described in detail in table 1 below.

TABLE 1 Compositions TM1 CA1 CA2 CA3 CA4 CA5 Carbon black (1) — 50 — — —— Carbon black (2) 50 — 50 50 50 50 Resin (3) 10 10 — 10 — 20 Resin (4)— — — — 10 — Z score 40 79 86 88 86 87 (1) N234 sold by the companyCabot Corporation (CTAB 115 m²/g) (2) N134 sold by the company CabotCorporation (CTAB 135 m²/g) (3) polylimonene resin (“OPPERA373N” fromthe company Exxon - Tg = 44° C.) (4) polylimonene resin(“SYLVAATRAXX4101” from the company Arizona - Tg = 72° C.)

The properties measured before and after curing at 150° C. for 40minutes are given in table 2 below.

TABLE 2 Compositions TM1 CA1 CA2 CA3 CA4 CA5 Properties before curingMooney 77 58 71 56 57 44 Properties after curing Stress at break 64.958.1 49.8 65.1 67.8 66.2 at 60° C. (MPa) Elongation at 287 263 180 250252 280 break at 60° C. (%) Energy at break 186 153 91 163 171 185tan(δ)_(max) 0.12 0.11 0.12 0.11 0.11 0.09

It is noted that the compositions CA3, CA4 and CA5 in accordance withthe invention, having a high Z score (greater than or equal to 70), andalso a black having a CTAB greater than or equal to 130 m²/g and aplasticizing hydrocarbon resin in accordance with the invention (with adifferent resin nature and different contents), make it possible,surprisingly, to notably improve the processability of the composition(lower Mooney value) compared with a control composition TM1, withoutdegrading the properties at break (stress, elongation, energy), contraryto the composition CA1 (comprising a carbon black with a CTAB specificsurface area of less than 130 m²/g) which improves the processabilitybut degrades the properties at break and contrary to the composition CA2which has degraded properties at break and an inferior processability(equivalent to TM1).

Thus, it is observed that it is this specific compromise of dispersionof the filler in the elastomeric matrix, of nature of the filler and ofpresence of plasticizing hydrocarbon resin which surprisingly makes itpossible to produce an improvement in the processability of thecomposition without degrading the other properties of the mixture.

1. A process for preparing a composition comprising: at least one dieneelastomer, a reinforcing filler comprising at least carbon black havinga CTAB specific surface area greater than or equal to 130 m²/g, aplasticizing hydrocarbon resin having a glass transition temperature,Tg, which is greater than 20° C. and the softening point which is lessthan 170° C., and a crosslinking system, wherein the filler is dispersedin the elastomeric matrix such that the dispersion has a Z score greaterthan or equal to 70, which comprises: incorporating all of theconstituents of the composition, with the exception of the crosslinkingsystem, in a mixer by thermomechanically kneading the whole mixtureuntil a maximum temperature of between 130° C. and 200° C. is reached,cooling the whole mixture to a temperature of less than 100° C.,subsequently incorporating the crosslinking system, kneading the wholemixture until a maximum temperature of less than 120° C. is reached. 2.The process according to claim 1, further comprising preparing a firstmasterbatch, comprising at least the diene elastomer and the carbonblack, and exhibiting a dispersion of the carbon black in theelastomeric matrix which has a Z score greater than or equal to 80,prior to incorporating all of the constituents of the composition in themixer.
 3. A process for preparing a composition comprising: at least onediene elastomer, a reinforcing filler comprising at least carbon blackhaving a CTAB specific surface area greater than or equal to 130 m²/g, aplasticizing hydrocarbon resin having a glass transition temperature,Tg, which is greater than 20° C. and a softening point which is lessthan 170° C., and a crosslinking system, which comprises: preparing afirst masterbatch, comprising the diene elastomer and the carbon black,and exhibiting a dispersion of the filler in the elastomeric matrixwhich has a Z score greater than or equal to 80, preparing the otherconstituents of the composition, with the exception of the crosslinkingsystem, into the first masterbatch in a mixer by thermomechanicallykneading the whole mixture until a maximum temperature of between 130°C. and 200° C. is reached, cooling the whole mixture to a temperature ofless than 100° C., subsequently incorporating the crosslinking system,kneading the whole mixture until a maximum temperature of less than 120°C. is reached.
 4. The process according to claim 3, wherein the firstmasterbatch is produced in the liquid phase from at least one elastomerlatex and a dispersion of carbon black.
 5. The process according toclaim 4, wherein the first masterbatch is produced by: feeding acontinuous stream of a diene elastomer latex to a mixing zone of acoagulation reactor defining an elongate coagulation zone extendingbetween the mixing zone and an outlet orifice, feeding a continuousstream of a fluid comprising a filler under pressure to the mixing zoneof a coagulation reactor to form a coagulum, drying the coagulum,thereby recovering the first masterbatch.
 6. The process according toclaim 1, wherein the diene elastomer is selected from the groupconsisting of polybutadienes, natural rubber, synthetic polyisoprenes,butadiene copolymers, isoprene copolymers, and blends of theseelastomers.
 7. The process according to claim 6, wherein the dieneelastomer is a natural rubber.
 8. The process according to claim 1,wherein the content of carbon black ranges from 20 to
 80. 9. The processaccording to claim 1, wherein the content of plasticizing resin rangesfrom 2 to 35 parts per hundred parts by weight of elastomer.
 10. Theprocess according to claim 1, further comprising introducing aninorganic filler and/or a second elastomer into the compositionsimultaneously with the other constituents.
 11. The process according toclaim 1, further comprising introducing an inorganic filler and a secondelastomer into the composition in the form of a specific masterbatchprepared beforehand.
 12. The process according to claim 1, furthercomprising introducing an inorganic filler and a second elastomerseparately into the composition, the inorganic filler being introducedbefore or after the second elastomer.
 13. The process according to claim12, wherein the introduction of the inorganic filler and/or of thesecond elastomer is offset in time by a few tens of seconds to a fewminutes relative to the introduction of the first masterbatch into themixer.
 14. A tire or semi-finished product comprising at least onecomposition according to claim
 1. 15. A masterbatch based on: at leastone diene elastomer, reinforcing filler comprising at least carbon blackhaving a CTAB specific surface area greater than or equal to 130 m²/g, aplasticizing hydrocarbon resin, having a glass transition temperature,Tg, which is greater than 20° C. and a softening point which is lessthan 170° C., wherein the filler is dispersed in the elastomeric matrixsuch that the dispersion has a Z score greater than or equal to
 70. 16.The masterbatch according to claim 15, which is obtained from a firstmasterbatch comprising at least the diene elastomer and the carbonblack, and wherein the dispersion of the carbon black in the elastomericmatrix of the first masterbatch has a Z score greater than or equal to80.
 17. A tire or semi-finished product comprising a masterbatchaccording to claim
 15. 18. A masterbatch based on: at least one dieneelastomer, a reinforcing filler comprising at least carbon black havinga CTAB specific surface area greater than or equal to 130 m²/g, aplasticizing hydrocarbon resin, having a glass transition temperature,Tg, which is greater than 20° C. and a softening point which is lessthan 170° C., which is obtained from a first masterbatch comprising atleast the diene elastomer and the carbon black, and wherein thedispersion of the carbon black in the elastomeric matrix of the firstmasterbatch has a Z score greater than or equal to
 80. 19. Themasterbatch according to claim 18, wherein the first masterbatch isobtained by mixing in the liquid phase from a diene elastomer latex andan aqueous dispersion of carbon black.
 20. A tire or semi-finishedproduct comprising a masterbatch according to claim
 18. 21. The processaccording to claim 2, wherein the first masterbatch is produced in theliquid phase from at least one elastomer latex and a dispersion ofcarbon black.
 22. The process according to claim 21, wherein the firstmasterbatch is produced by: feeding a continuous stream of a dieneelastomer latex to a mixing zone of a coagulation reactor defining anelongate coagulation zone extending between the mixing zone and anoutlet orifice, feeding a continuous stream of a fluid comprising afiller under pressure to the mixing zone of a coagulation reactor toform a coagulum, drying the coagulum, thereby recovering the firstmasterbatch.